The blood compatibility of porous materials being perfused with physiologic fluids will be studied. The range of porosity and materials variables within which platelet and protein adhesion can be prevented at reasonable perfusion rates will be examined. Measured minimum perfusion rates for incipient platelet deposition of a perfusion surface will be compared with rates calculated from diffusion theory. The effects of controlled pulsatile flow of perfusant on platelet adhesion to sticky and non-sticky porous materials will be investigated.